The essay is based on the inventory of the Friedrich Gottreich Striebel Collection preserved in the Historical Archives of the Fabbrica di San Pietro in the Vatican. The collection consists of a single bundle containing fourteen manuscript fi les. It represents the results of the activities of the Saxon Friedrich Siegmund Striebel during the years 1744-1749, when he collaborated with the chemist-alchemist-glassmaker, Alessio Mattioli. Mattioli’s discoveries determined the composition of the enamels used for the mosaics decorating St Peter’s Basilica in the Vatican. In 1806, the Collection was acquired by the Fabbrica di San Pietro, which at one time oversaw an Italian translation of the material and more recently its reordering. This essay presents the circumstances under which the manuscripts were composed, focusing on the particular quality, signifi cance and structure of the material, as well as its history. The Collection, closely tied to the history of mosaics, also includes information of interest to a variety of other disciplines, such as chemistry, botany, mineralogy and numismatics. The article also highlights the Collection’s valuable and unexpected evidence for a complex web of diplomatic communications between the Saxon Court and certain important fi gures in the Roman Curia, bearing upon religious, political and artistic issues. Finally, the essay makes an initial attempt to reconstruct the biography of the author of the Collection, hitherto little known to experts. He has remained obscure despite more than twenty years of activity in Rome and Italy as a painter, mosaic artist, and art dealer for the famous Gallery of Dresden, also known as the Old Masters Picture Gallery.